GRE Prep Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
A set has an average (arithmetic mean) of 42 and a standard deviation
[#permalink]
21 Sep 2021, 01:15
21 Sep 2021, 01:15
Expert Reply
00:00
Question Stats:
55% (00:36) correct
44% (01:06) wrong based on 18 sessions
Hide Show timer Statistics
A set has an average (arithmetic mean) of 42 and a standard deviation of 1.8. Which of the following values is two standard deviations away from the mean?
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Re: A set has an average (arithmetic mean) of 42 and a standard deviation
[#permalink]
21 Sep 2021, 06:10
21 Sep 2021, 06:10
Carcass wrote:
A set has an average (arithmetic mean) of 42 and a standard deviation of 1.8. Which of the following values is two standard deviations away from the mean?
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
A. 36
B. 38.4
C. 40.2
D. 43.8
E. 75.6
A little extra background on standard deviations above and below the mean
If, for example, a set has a standard deviation of 4, then:
1 standard deviation = 4
2 standard deviations = 8
3 standard deviations = 12
1.5 standard deviations = 6
0.25 standard deviations = 1
etc
So, if the mean of a set is 9, and the standard deviation is 4, then:
2 standard deviations ABOVE the mean = 17 [since 9 + 2(4) = 17]
1.5 standard deviations BELOW the mean = 3 [since 9 - 1.5(4) = 3]
3 standard deviations ABOVE the mean = 21 [since 9 + 3(4) = 21]
etc.
-----------------------------
For this question, if the standard deviation is 1.8, then two standard deviations = (2)(1.8) = 3.6
So, two standard deviations BELOW the mean = 42 - 3.6 = 38.4
And two standard deviations ABOVE the mean = 42 + 3.6 = 45.6
This means there are two correct answers.
Now check the answer choices for one of the two possible answers.
Answer: B
gmatclubot
Re: A set has an average (arithmetic mean) of 42 and a standard deviation [#permalink]
21 Sep 2021, 06:10
Moderators:
